Clutch systems are used in motor vehicles for separating the engine and gearbox. In modern vehicles, virtually exclusive use is made of friction clutches or hydrodynamic transmissions. In the customary friction clutch, force-transmitting connection between the shaft from the engine and the shaft entering the gearbox is established by means of one or more disks pressed against one another, with at least one clutch disk connected to the shaft entering the gearbox, which has linings on both sides, being located between the flywheel of the engine and a clutch pressure plate. When the clutch pedal is depressed, the pressure plate is pushed away from the clutch disk against the spring force of the disk spring, as a result of which the clutch disk is released. The connection between the engine and the gearbox is thereby interrupted.
The magnitude of the torque which can be transmitted depends on the area and the diameter of the clutch disk and on the spring force of the disk spring. For large torques, clutch systems having a relatively large friction area or multidisk clutches are therefore used. The clutch disk is, especially on starting, subject to wear by rubbing and is heated by the friction.
In view of this prior art, it is an object of the invention to provide clutch systems which can transmit large torques at small construction sizes. Preference is given to single-disk systems which have relatively small friction areas.
Friction pairings with ceramic materials, in particular fiber-reinforced ceramic materials, are known. When used as brake disks, high heat resistance and a coefficient of friction which has a low dependence on the load are required. In the case of clutch systems, high static friction and high torsional stiffness are desired.
In WO 93/11185, clutch disks are disclosed which have friction surfaces composed of a plurality of layers which alternately contain continuous carbon fibers and short carbon fibers and in each case pitch as impregnant.
In WO-A 01/55611, multidisk clutches immersed in an oil bath are disclosed, in which steel disks lined with braided continuous carbon fibers act against steel disks whose friction surface is coated with a thin layer of nickel powder.
The application of continuous carbon fibers or textiles made of these is complicated. Furthermore, the experiments on which the invention is based have shown that the preferential orientation of the fibers in the plane of the linings produced from continuous carbon fibers or textiles in which these are present is relatively unfavorable for achieving a high static friction. For this reason, linings for clutch disks which are simple to manufacture and display high static friction values are desirable.
In DE-A 199 39 545 clutch disks are disclosed which are provided with friction linings comprising silicon carbide reinforced with carbon fibers. It can also be provided for the flywheel and pressure plate forming a friction pairing with the linings to be made of silicon carbide reinforced with carbon fibers. Otherwise, nothing is said about the type of material used.